Surface acoustic wave (SAW) sensors are employed in a wide variety of applications for sensing one or more parameters within an environment. In the automotive industry, for example, such devices have been used to monitor tire pressure and temperature, and to detect finger pressure in keyless entry systems. Because SAW sensors are typically fabricated using photolithographic techniques similar to that used in the semiconductor industry, such devices can be made reliably, making them desirable in those applications demanding a high level of precision and low cost. Other factors such as high sensitivity, low noise, size, and imperviousness to many environmental factors also make SAW sensors desirable in many applications.
More recent trends in the art have focused on the fabrication of wireless and passive MEMS SAW sensors. In contrast to more traditional, active sensors that rely on the use of a battery or capacitor as a power source, wireless and passive MEMS SAW devices are useful in those applications where the harsh environment may prevent the presence of a human operator, or where the presence of wires and/or a power supply may be inappropriate. In the chemical industry, for example, such wireless and passive SAW sensors can be used for extended periods of time to sense pressure, temperature, the existence of chemicals, or other desired parameters in harsh environments where gasses or chemicals may prevent human interaction. In medical applications, such wireless and passive SAW sensors can be used to non-invasively (e.g. using liquid-sensitive acoustic modes) monitor glucose or other desired fluids within the body for relatively long periods of time without the need for replacing batteries.